In the near future, the feature One Tunnel Solution/Direct Tunnel (OTS/DT) will be introduced into 3GPP. However, there are no real solutions to the problems regarding Error Indication handling.
The procedure that will most likely be used during Error Indication scenarios when DT/OTS is active is either Network Initiated Service Request (using Protocol Data Unit (PDU) Notification) or Gateway GPRS Support Node (GGSN) Initiated Packet Data Protocol (PDP) Context modification.
When using the proposed PDU Notification procedure combined with DT/OTS also a critical state machine is introduced in the GGSN, between steps 2 and 7 in FIG. 1. FIG. 1 illustrates signalling diagram for the Network Initiated Service Request Procedure which is used for reestablishment of RABs and the steps comprise:                1) The GGSN receives a downlink PDP PDU for a User Equipment (UE) in PMM-IDLE state.        2) The GGSN sends a PDU Notification Request message to the SGSN related to the PDP context. The SGSN returns a PDU Notification Response (Cause) message to the GGSN in order to acknowledge that it requests the UE to re-activate the PDP context(s).        3) The SGSN sends a Paging message to the Radio Network Controller (RNC). The RNC pages the UE by sending a Paging message to the UE.        4) The UE sends a Service Request message to the SGSN. Service Type specifies        5) The SGSN performs a security mode procedure.        6) If resources for the PDP contexts are to be re-established, the SGSN sends a Radio Access Bearer Assignment Request (including RAB ID(s), GGSN TEID(s), QoS Profile(s), GGSN IP Address(es)) message to the RNC.        7) Having received the IP address(es) and the TEID(s) from the RAN the SGSN sends an Update PDP Context Request (including RAN Address, RAN TEID, QoS Negotiated) message to each GGSN concerned. Each GGSN updates its PDP context fields and returns an Update PDP Context Response (TEID) message. The tunnel between RAN and the GGSN is re-established.        8) The GGSN sends the downlink packet.        
The existing problems include:                The proposed procedure will use unnecessary signalling capacity over Gn, which can cause overload of the backbone.        Risk of overloading the GGSN when having the proposed Update PDP Context Request bursts.        Risk of overloading the Serving GPRS Support Node (SGSN) when handling the proposed Update PDP Context Request bursts.        Risk of losing downlink payload packets before the SGSN and GGSN are synchronised.        